Casting process and machine



Feb. 2, 1960 c. GOODWIN ETAL 2,923,040

CASTING PROCESS AND MACHINE 4 Sheets-Sheet 1 Filed July 16, 1956 .lfil.

INVENTORS CARL L. GOODWIN WILLIAM. T. ENNOR ,4 TTaR/VE y Feb. 2, 1960 c.L. GOODWIN F 2, 3, 40

CASTING PROCESS AND MACHINE 4 Sheets-Sheet 3 Filed July 16, 1956 N mm wOD /y r TOE 5 M M V ma m A n r L r T A CW Feb. 2, 1960 c. L. GOODWIN'ETAL 2,923,040

7 CASTING PROCESS AND MACHINE Filed July 16, 1956 4 Sheets-Sheet 4INVENTORS CARL L. GOODWIN WILLIAM T. ENNOR ,4 rramvs r UnitedStatesPatent CASTING PROCESS AND MACHINE Carl L. Goodwin, Bay Village, Ohio,and William T.

Ennor, Oakmont, Pa., assignors to Aluminum Company of America, NewKensington, Pa., a corporation of Pennsylvania Application July 16,1956, Serial No. 598,025

11 Claims. (Cl. 22-73) This invention relates to the rapid production ofchill castings of the light metals, aluminum, magnesium and those alloyswherein these elements constitute more than 50% by weight of thecomposition. The term chill casting as used herein refers to castingsproduced in molds, usually made of metal, which cause a rapidsolidification of the molten metal poured therein. The cast products maybe utilized in the as-cast condition or they may serve as stock for thefabrication of wrought articles, especially those made by the extrusionor forging processes.

To gain high production rates in the manufacture of relatively smallcastings, it has been conventional to simultaneously cast a large numberof units in a single mold and subsequently sever each casting from thecommon runner or gate and trim off any risers. Separate castings can bemade by the die casting process at a rapid rate but it is stillnecessary to sever the casting from the gates and risers. Also, diecastings are apt to contain minute voids which are undesirable where thecasting is to be subsequently worked.

Castings have not been used to any extent as stock for the production ofimpact extruded articles because they have been considered to lack thesoundness and uniformity of the conventional rolled plate and rod usedfor this purpose and'have not possessed the close dimensional tolerancesrequired in extrusion slugs. As is well known, impact extrusion slugsare blanked from plate stock, usually in a gang press, or they are cutfrom rolled or extruded rod. The latter practice is generally used wherethe height of the slugs exceeds the thickness of plate which can beeconomically blanked. It is obviously expensive to cast ingots and rollthem to plate or rod dimensions or to extrude the ingots into rod beforeslugs can be cut from the worked stock. Where plate is employed there isthe added cost of a high scrap loss resulting from unused portions ofthe plate. The sawing which is required, when rod is used, is anexpensive operation and it generates a scrap material. No castingmethods have been devised whereby single castings can be made at a highproduction rate that have the close tolerances required for impactextrusion slugs, a sound ness substantially equivalent to that of rolledplate, and which are substantially free from the conventional gates andrisers.

One of the objects of our invention is to provide a method of makingexceptionally sound individual castings of light metals which requirelittle or no trimming preparatory to being used. Another object is toprovide a method of making dimensionally accurate, sound individualcastings of light metals at high production rates. A further object isto provide a method of making in chill molds at a high production ratelight metal castings which are substantially free from shrinks, voids orentrapped gas. A particular object is to provide a method for castingslugs suitable for use in making impact extrusions and forgings. Stillanother object is to provide a method of making individual chillcastings or light metal by quick progressive freezing of the moltenmetal tion.

' These and other objects are achieved by the method and with theapparatus described below, certain embodiments of the apparatus beingshown in the accompanying partially schematic drawings wherein Fig. 1 isa top plan view of a casting machine for making solid cast bodies and anassociated device for transferring castings from the machine;

Fig. 2 is a side elevation of the casting machine taken on section 11-11of Fig. 1 and a partial view of th transfer device;

Fig. 3 is a plan view of a casting machine for making hollow cast bodiesand an associated device for trans-' ferring castings from the machine;3

Fig. 4 is a side elevation of the machine shown in 3 taken on line IV-IVand a partial view of the transfer device;

Fig. 5 is a cross section of the machine on a reduced scale taken online VV of Fig. 4; and

Fig. 6 is another cross section of the machine, also on a reduced scale,taken on a lower plane on line VI--VI of Fig. 4.

In our method, the molten metal is fed under external atmosphericpressure into the bottom of a horizontally parted mold which ispartially evacuated during the filling operation. The lower mold portionis held in continuous contact with the molten metal body from whichmetal is withdrawn to fill the mold cavity while the upper portion isartificially cooled. The bottom of the mold cavity is thus maintained ata relatively high constant temperature and the upper part is kept at amuch lower temperature. By holding the mold bottom in contact with themolten metal the latter has but a short distance to rise to fill themold cavity. As a result of such bottom feeding and short travel of themolten metal there is little or no turbulence, splashing or surging suchas characterizes the conventional methods of filling molds. Chilling ofthe molten metal commences at the sides and top of the mold cavity andprogresses toward the bottom gate. The chilling of the mold ispreferably elfected by circulation of coolant at least within the sidewalls of the mold body. As soon as freezing begins within the gateaperture the upper portion of the mold with casting therein is raisedabove the bottom portion which remains in' contact with the molten metaland the casting is ejected from the raised mold portion onto suitablemeans for transferring the casting to a discharge station.

The partial evacuation of the mold cavity and sub sequent ejection ofthe casting therefrom under positive air pressure is elfected throughconnection to suitable pumps or other means of providing the desiredpressure with a system of valves to control the evacuation and admissionof air. Initially the mold cavity is partially evacuated, the pressurebeing reduced only about O;l to 1.5 pounds per square inch belowatmospheric pressure, because such a small reduction in pressure is allthat is required to bring about a complete filling of the mold cavity.In the production of certain castings it is desirable to further reducethe air pressure to create a higher vacuum at the top of the mold cavityto hold the casting in the mold when the latter is raised. In some casesthis further reduction in pressure is made just after the metal hasstarted to freeze so as to maintain the cast body in closer contact withthe top of the mold and thereby increase the rate of heat transfer from.the top of .the cast .body to the mold; Upon comple- Patented Feb. 2,1960,

tion of freezing of the casting, the upper portion of the mold iselevated from the base, and a positive air pressure applied at the topof the mold cavity in place of the reduced pressure with the result thatthe casting is ejected from the mold. It will be appreciated that theadmission and extraction of air from the mold cavity can be effected byautomatic or semi-automatic means which are integrated with the movementof the upper portion of the mold. Under such conditions a complete cycleof casting, ejection and transfer of the cast product can be generallycompleted within a period of from S to 200 seconds depending upon thesize of the casting. The light metal castings produced in this mannerhave been found to possess a soundness, density and dimensional accuracysubstantially equivalent to that of stock cut from rolled plate or rod.The casting process and the machine are well adapted to the productionof light metal cast bodies at a high rate, especially if a plurality ofmold cavities are provided in one machine and all are filledsimultaneously. Although the process and machine are particularly suitedto the production of small castings such as for impact extrusion, largercastings can also be made.

A unique feature of the process described above is derived from therelative orientation of the solid metal (i.e. the casting) to the sourceof molten metal. Because the solid metal is above the molten metal, thetwo may be parted easily without use of special valves to stop off theflow of molten metal. A further important and unique feature of theprocess is to be found in the fact that the metal feeding system isself-metering and supplies only enough metal to completely fill and feedthe mold cavity. These features simplify the casting procedure byeliminating the special molten metal pumps, valves and metering devicesfrequently employed to provide automatic pouring in conventionaltop-delivery casting practice.

Referring to the controlling features of our process in greater detail,it is essential that the molten metal be fed to the bottom of the moldcavity and that it be moved as short a distance as possible from thesource of supply to the mold cavity thus attaining certain advantages infilling the mold cavity as described hereinabove as well as providingfor a quick transfer of metal to the mold cavity. This may beaccomplished by maintaining the lower portion of the mold in astationary position in contact with the body of molten metal whichserves as the source of supply, but the mold is not submerged in themolten metal to the extent that the molten metal flows into the moldcavity under hydrostatic pressure. Moreover, by keeping the mold bottomin continuous contact with the body of molten metal it is maintained ata constant relatively high temperature close to that of the moltenmetal. In this manner the gate opening does not become clogged withfrozen metal, the molten metal enters the mold cavity with a minimumloss of heat thereby insuring proper filling of the cavity withoutpremature freezing of the metal and a nearly constant temperaturegradient is established between the bottom of the mold and the upperportion. By keeping the bottom of the mold in a stationary positionthere is no disturbance of the metal bath as would occur if the mold orparts thereof were moved into or out of the bath. Furthermore, bysubmerging the bottom of the mold in the metal bath and feeding the moldcavity from below the surface of the metal bath through a gate in thebottom of the mold cavity, the metal entering the mold cavity issubstantially free from dross and oxide skin.

To effect rapid and directional freezing of the metal within the mold, asharp temperature differential is established and maintained between theupper and lower portions thereof. Contrary to the customary top pouringpractice we supply hot liquid metal to the bottom of the mold cavity andcompensate for any shrinkage resulting from solidification by drawingmolten metal upwardly from the source of supply through the gate. Thetemperature differential is created by artificially cooling the upperportion of the mold and maintaining the bottom portion close to themelting point of the metal being cast. A satisfactory practice is tomaintain the temperature of the upper mold portion between about and 400F. while keeping the bottom, which is in contact with the molten metal,at about 900 to l30 0 F. The metal within the mold will still freezeeven though the bottom plate temperature is above the melting point ofthe metal since freezing progresses so rapidly from the top and sidewalls of the mold. The artificial cooling is conveniently done bycirculating water inchannels within the mold wall or by providing waterjackets around that part of the mold. To effect the desired directionaland progressive freezing it is usually advisable to maintain atemperature differential of between about 500 and 1200 F. between'theupper portion of the mold and the bottom thereof. Under thesetemperature conditions, freezing of the molten metal can usually becompleted within a period of 3 to seconds depending upon the size of thecasting, the alloy and the temperature of the incoming metal. In anycase, the freezing must progress fast enough to insure a finemetallurgical structure, a coarse structure being undesirable.

In respect to filling of the mold cavity, this is accomplished byatmospheric pressure exerted on the surface of the body of molten metalin the holding pot and by partial evacuation of the mold as has beenmentioned above. We have found that only a slight reduction in pressurewithin the mold cavity is necessary to cause the liquid metal to flowinto it. Ordinarily, the air pressure within the cavity need be reducedonly 0.1 to 1.5 p.s.i. below normal atmospheric pressure to effect acomplete filling of the mold. In our preferred practice the lowestpredetermined air pressure is not immediately established within themold cavity prior to the introduction of molten metal, but rather it isgradually approached. Thus, the initial reduced pressure is sufficientto start filling the mold but the maximum reduction in pressure is onlyestablished after the cavity has been partially filled with the moltenmetal. Such a gradual change in pressure offers the advantage ofavoiding any spurting of molten metal into the mold cavity and itassures an adequate and uniform lower fillet radius at the bottom of thecasting. In addition, filling of the mold cavity in this manner tends toreduce the flow lines around the lower periphery of the cast product. Inextreme cases such flow lines may be objectionable.

In the production of certain castings, especially those which are'solid, i.e. there are no cored portions, it is sometimes desirable tofurther reduce the air pressure at the top of the mold cavity just afterthe mold has been filled and a solidified shell has been formed. Such afurther reduction in air pressure serves to draw the casting closer tothe top wall of the mold and by thus reducing the insulating air gapbrings about an increase in the rate of heat transfer and rapidity ofsolidification of the balance of molten metal in the casting. The latteradvantage is only realized, of course. if the higher vacuum is appliedbefore all of the metal has frozen. The reduction in air pressure justreferred to is on the order of from 10 to 14 p.s.i. below atmosphericpressure.

When all of the metal within the mold cavity has frozen andsolidification begins in the gate leading to the mold cavity, the upperportion of the mold with the casting therein is raised from the bottomportion and the cast body is ejected from the raised portion of themold. The size of the protuberance extending into the gate is determinedby the time which is permitted to elapse before the mold is raised. Bycareful timing only a very small protuberance is developed which can beeasily removed, or if small enough, it maybe disregarded. The reducedair pressure at the bottom of the casting is, of course, terminated whenthe upper mold portion and casting are raised and the vacuum at the topof the mold cavity is ended when the casting is to be ejected. Suchejection may be conveniently effected by pneumatic means, as by applyingcompressed air to the top of the mold cavity, or by mechanical means, aswith ejector pins. Continuation of the reduced air pressure as the uppermold portion and casting are being raised is generally desirable toretain the casting in place.

A machine for producing castings at a high rate of output includes atwo-part mold and the mechanism for operating it in conjunction withmeans for controlling the air pressure within the mold cavity. The mold,made of any suitable heat resistant material such as a ferrous alloy,consists of an upper or top portion which defines the top and side wallsof the mold cavity, and a bottom portion composed of a plate which formsthe bottom of said cavity. The mold is therefore parted in a horizontaldirection, the parting line preferably being at the surface of thebottom plate. At least one gate opening is provided in the plate forpassage of molten metal into the mold cavity. Where a hollow casting isto be produced, it is desirable to employ two or more symmetricallydisposed gates in order to provide rapid and equal flow of metal intoall parts of the mold cavity. The diameter or cross sectional area ofthe gates must be large enough to permit the flow of metal therethrough,prevent undue freezing of metal therein and at the same time not solarge as to permit the formation of protuberances which are difiicult toremove.

The top or upper portion of the mold is movable in a vertical direction,while the bottom portion is maintained in a stationary position. Thismovement of the upper portion of the mold body is essential to operationof the mold to permit ejection of the casting. In the form of themachine for producing hollow castings a core member is provided which ismovable with respect to the top and side walls of the mold. Suchrelative movement is necessary prior to ejection of the casting from themold.

The evacuation af air from the mold cavity and admission of air theretois effected through ducts leading to vents at the top and bottom of thecavity which are so narrow that the molten metal will not enter themeven though air is withdrawn through them. A very satisfactoryarrangement is that of locating the vents at the junctions or co'rnerswhere the side wall of the mold joins the top and bottom members. Thevents may be in the form of separate openings or a continuous openingaround the periphery of the mold cavity. By providing vents at thecorners, especially at the top of the mold cavity, the cavity isproperly filled with metal and any voids or other imperfectionsassociated with poor filling are avoided.

Associated with the mold are means for supporting it on a framework andfor moving the upper portion in sequence with respect to theintroduction of molten metal and ejection of the casting from the mold.Suitable pneumatically or hydraulically operated cylinders mounted onthe frame offer convenient and efiicient power means.

A transfer device for receiving the castings ejected from the mold andtransporting them to a discharge station also forms a part of thecasting machine inasmuch as it must function in sequential relationshipto the mold operations.

Specific forms of the apparatus described above are illustrated in theaccompanying figures, Figs. 1 and 2 showing a machine for making solidcylindrical castings while Figs. 3 to 6 set forth a machine for castinghollow cylindrical bodies. A plan view of the first mentioned machine isto be seen in Fig. 1 where the casting unit is suspended above a metalholding pot and a device'at one side of the unit for receiving andtransferring the cast slugs ejected from the mold. The casting unit issuspended over a melting pet from a cap plate 14 resting upon ringmember 12 which in turn is carried on channel frame members 10. Thestationary bottom portion of the mold is bolted to the lower ends offour symmetrically disposed columns 16 which are attached by bolts attheir upper ends to the cap plate 14. The upper or movable part of themold assembly is supported from a crosshead 54 which slides on columns16 and is guided by sleeves 5S fixed to the crosshead. Posts having caps74- are rigidly attached to mold top plate 66 and pass through thecrosshead, connection thereto being made by compression springs as seenin Fig. 2. Movement of the crosshead is effected by air or hydrauliccylinder 18 mounted on the cap plate 14. The stationary or lower portionof the mold assembly is located within a circular opening in the metalpot cover 38, as more clearly seen in Fig. 2.

The device for receiving and transferring cast slugs may be integrallyconnected to the casting unit or it may be independently mounted topermit movement into or out of operating position. The device consistsof a rec- 'tangular bed frame 22 carrying a sliding frame 24 with tray26 positioned thereon and means for moving the frame and tray intoposition for receiving the cast slug dropped from the mold andretracting it from the receiving position. A convenient means for movingframe 24 and tray 26 consists of an air cylinder 32 mounted on auxiliaryframe 30 which is rigidly attached to the main frame 22 and operativelyconnected to the sliding frame 24 by rod 34. A cast slug 28 is to beseen resting upon tray 26 in retracted position.

A side elevation of the casting machine which shows more details and thestructural relationship of the various parts to each other is to be seenin Fig. 2 which is taken on line IIII of Fig. 1. The stationary bottomportion of the mold consists of a dish-shaped member, preferably made intwo parts, a bottom plate 44 with a gate opening 46 therein and anL-shaped upper part composed of a vertical wall section 48 and anoutwardly extending flange 50 for attachment to columns 16. The twoparts may be mechanically joined together in conventional manner, orthey may be welded if the structural material permits. Although thedish-shaped member can be of unitary construction, it is frequentlydesirable to make it in two parts so that the bottom plate can bereplaced when necessary. As a matter of practice it is usuallyadvantageous to coat at least the under side of the bottom plate with aconventional refractory coating to minimize attack by the molten metal.Generally, ferrous meals are suitable for construction of the mold andmold parts.

The upper or movable portion of the mold, suspended from the crosshead54, is composed of two parts, a vertical wall portion 64 and a topmember 66 rigidly joined thereto by mechanical means. Posts 68, forsupporting the upper mold portion from the crosshead 54, may be screwedinto top member 66, or they may be attached by these means to a base 70which in turn is joined to 66. The posts 68 are freely movable inopenings provided in the crosshead for this purpose. A resilientconnection with the crosshead is provided by a pair of compressionsprings 72 encircling the posts, one being located above the crossheadplate and the other below the plate. The upper spring is held in placebetween cap 74 on posts 68 and the crosshead, the spring preferablybeing seated in a slight recess in the plate to prevent displacement.The lower spring is similarly positioned between the plate 54 and thepost base 70. The springs serve to establish and maintain the alignmentand contact necessary between the upper and lower portions of the moldwhich is neces# sary to produce a tight seal when they are pressed together and to absorb the shock of contact between the moving andstationary mold elements as wellas any shock resulting from abruptmovement of the crosshead by the power cylinder 18.

The crosshead is maintained in proper alignment by means of guidesleeves 58 sliding on columns 16 having reduced threaded extensions 60for receiving lock nuts 62. The movement of the crosshead is effectedthrough connecting rod 52 which joins the crosshead to the plunger inpower cylinder 18.

With respect to the cooling of the side and top portions of the mold,spirally arranged internal tubes or channels 76 may be provided.Alternatively, a water chamber or jacket may be employed which extendsover substantially the same wall area. T provide such internal waterpassages it is usually desirable to make the mold wall or top in twoparts, to machine the channels or recesses therein and join the twoparts by any suitable means. The water passageways, of course, must beadequate to provide for rapid dissipation of heat from the mold andconsequently should be large enough to prevent any clogging orobstruction from any dirt or suspended particles that may be carried bythe water. The upper mold Parts may be made of any conventional ferrousmetal or other material which will withstand the repeated contact withmolten metal.

The air duct system for evacuating the mold cavity 67 and admitting airthereto consists of a portion which serves the top of the cavity and theother which serves the bottom thereof. Duct 78, which is confined to thetop mold member, extends inwardly from the outer edge of the member toan annular channel or groove 80 which encircles the mold cavity and isin close proximity to the cavity. The channel or groove 80 may bemachined or otherwise provided in the top surface of vertical moldsection 64 before the mold parts are assembled. Communication betweenthe channel 8t) and mold cavity 67 is provided by a narrowcircumferential vent 82, which is of such a small width that moltenmetal does not enter it under the reduced pressure conditions prevailingin the mold cavity during the filling thereof with molten metal.Provision of a vent around the entire circumference of the mold cavityhas been found to be very effective for withdrawing air and promoting aquick and complete filling of the cavity with molten metal. The ventalso provides for the quick and effective application of compressed airto the top of the casting to eject it from the mold. If ejector pins areemployed a vent may be provided around them and dispense with the upperduct system. The other portion of the duct system consists of a duct 84in the top mold member which registers with a vertical passageway 86 inthe side mold member. The duct 86 leads into an annular channel orgroove 88 which in turn communicates with the mold cavity through narrowvent 90. A rim or ridge 92 is provided at the outside edge of the bottomsurface of side member 64 to establish a seal with bottom plate 44 andprevent ingress of air from the surrounding atmosphere. Conventionalfittings 94 and hose are provided to connect the duets with regulatingvalves and air line to the pumps not shown.

In operating position the bottom plate 44 is partially submerged belowthe surface 42 of the body of molten metal in holding pot 20. As aresult of the submergence, molten metal rises in gate 46 almost to thetop of the plate 44.

The cast slug transfer device is mounted at an elevation such that themovable frame 24 with tray 26 can be advanced to a position to receiveslugs ejected from the mold when in the fully raised position. Thetransfer device, of course, must be located to pass between columns 16and to clear the top of the dish-shaped bottom member.

A modification of the foregoing machine, which is adapted to producehollow castings, is shown in Figs. 3 to 6. From the plan view appearingin Fig. 3 it will be apparent that the casting unit is supported in thesame manner as the one described above and that the same type oftransfer device is used to receive and remove castings dropped from themold. It is to be noted, however, that only three symmetrically spacedcolumns 16 are employed to sup-port the unit from cap plate 14. Theother supporting columns and posts, 134, 68, 144 and 156 are alignedwith the main columns 16. Mounted on the cap plate 14 is a powercylinder 18 which raises and lowers the entire upper mold assemblyincluding the core elements. Below the'main cap plate 14 is a secondone, 132 with which the power cylinder is connected and which supportsthe upper mold assembly. A third cap plate 148, smaller than 132,supports the core actuating power cylinder, not seen in this view, andbelow it is plate 154 attached to the movable core member.

Details of construction and the relationship of the various parts of themachine to each other are illustrated in Figs. 4, 5 and 6. In thesectional view appearing in Fig. 4, it will be seen that the stationaryand lower portion of the mold consists of a dish-shaped member as in themachine described hereinabove. The dish is preferably made in two parts,a bottom plate 44 and an L-shaped upper part, the horizontal flangeportion 50 serving as the base for attachment of the supporting columns16. In the production of hollow castings it is advisable to provide aplurality of gates to obtain rapid and uniform filling of the moldcavity. In the present instance four symmetrically spaced gates 46 arelocated in the bottom plate 44, only two of the gates being seen in thefigure.

The upper, or movable portion of the mold, which cooperates with thebottom plate to form the mold cavity 99, is composed of side wall member64, top member 98 and liquid cooled c'ore member 100. The side wallmember 64 may be conveniently attached to top mem-' ber 98 by a longshank bolt, as shown, or the two parts may be joined in other mechanicalmanner. The mold top member 98 is firmly attached to cylindrical coreguide 142 by any convenient means such as a long through bolt. Tomaintain the proper alignment of the mold parts with the guide 142, acollar 162 is provided which encircles the mold top 98 and bears againstboth the guide and mold side wall. The collar 102 need not be rigidlyattached, but should be snugly fitted to maintain the desired alignment.

The core assembly consists of a slightly tapered (less than 1) liquidcooled tip which is an extension of the main core body 122 that moves inguide 142. The upward movement of the core is limited by a stop 146 inthe shape of a ring which is secured to the top of the guide cylinder142 by the same through bolt which connects the guide to the top moldmember 98. It will be appreciated that the stop may be attached in othermanners and that the stop may assume other forms than that of a ring.The stop 146 is located only a short distance above the ,core member inits lowermost ]'JO sition since because of the taper of the core it isonly necessary to raise the core less than the height of the casting toseparate it from the casting preparatory to ejecting the cast body fromthe mold. Three symmetrically disposed posts 144, rigidly attached attheir lower ends to ring 146, or the guide 142, carry the cap plate 148on which power cylinder 150 is mounted. The power cylinder, which may bepneumatically or hydraulically operated, raises and lowers the core bymeans of rod 152 attached to the plunger and bolted to plate 154. Theplate 154, spaced from the core body 122, is connected thereto by postsor legs 156 rigidly attached to both the plate and core body. Therelative position of the supporting members with respect to thecrosshead and core assembly are clearly seen in the sectional view inFig. 5, also the spacing of the mold from the crosshead.

The core tip 100 is cooled by a liquid, preferably water, circulated inchamber 128 which is divided into l 9 substantially two portions bybaffle 126 that extends across the chamber and almost to the bottomthereof. The baffle, as shown in Fig. 6, is an extension of plug 158fitted in the top of the bore forming chamber 128. The water or othercoolant is admitted to the chamber through tube 130 and duct 124 and isdischarged through a similar duct and tube. The tubes 130 are arrangedto pass through the cap plate 154 in order to facilitate makingconnections with a source of water.

The whole upper mold assembly just described is suspended from cap plate132 by three symmetrically spaced columns 134 bolted at their lower endsto crosshead 136. As previously stated the movement of the crosshead 136and assembly supported therefrom is effected by power cylinder 18through connecting rod 52 attached to cap plate 132. The crosshead isguided on columns 16 by sleeves 58 as in the machine described above. Acentral opening 138 is provided in the crosshead to accommodate theupper mold assembly, the latter being resiliently connected to thecrosshead through compression springs 72 which surround supporting posts68. The posts 68 are mechanically attached to the circular flange 140which is joined to the guide 142. The upper compression spring ispositioned between the post cap 74 and the crosshead while the lowerspring is mounted between the flange 140 and the crosshead.

The admission and evacuation of air to the top of the mold cavity iseffected through duct 104, annular groove 106 and vents 107 and 108. Inthe production of hollow castings it is essential that provision be madefor withdrawal and admission of air adjacent the core as well as theouter mold wall. To this end a small recess 109 is provided in the maincore body 122 which registers with duct 104 and terminates at-vent 107so that when assembled with top plate 98 there is a passageway from duct104 to the vent 107. Both vents 107 and 108 are situated at the uppercorners of the mold cavity and are of such a narrow width that themolten metal does not enter them as the mold cavity is filled. The otherduct 110 communicates with the bottom of the mold cavity through avertical passageway 112 in mold wall 64. The passageway 112'terminatesin annular groove 114 which is in communication with the mold cavitythrough vent 116. A slight rim 118 is provided at'the outer edge of theside wall member 64 to effect a seal against the admission of air to themold cavity during the period of evacuation. Fittings 120 are threadedinto ducts 104 and 110 and the tubes associated therewith provide aconnection to control valves and'the air and vacuum pumps not shown.

The sectional view seen in Fig. 6 shows the water passages to the corechamber 128, the mold cavity around the core and the air passagewaysleading to the mold cavity.

A cast slug transfer device of the same character as that shown in Fig.2 may be employed to receive and remove slugs ejected from the mold.

To conduct the process and operate the machines referred to above, theholding pot 20 is filled with molten metal to the desired level 42 whichis preferably maintained throughout the series of casting operations.This level maybe maintained in known manner such as by the manualladling of a small quantity of metal at intervals, by gradually pouringmetal from a holding ladle or by an automatic float-control arrangement.The casting machine may be lowered into place on the supportingframework over the holding pot, or the latter may be elevated to thedesired level. In any event, the bottom plate 44 of the mold must bepartially submerged in the metal bath 40 but care must be exercised toavoid immersing it to a depth such that the molten metal runs into themold cavity under hydrostatic pressure. To facilitate commencement ofcasting it is advisable to preheat the bottom plate before submerging itin the metal bath but, of course, the heating may be etfected bysubmerging the cold plate in the metal bath. The plate; however, shouldattain a temperature of between about 900 and 1300 F. to producesatisfactory castings. Also, the circulation of coolant is started inthetop and side wall members of the mold and core, if one is employed,before casting operations are commenced. The upper mold portion, whichis initially at room temperature, becomes heated as the castingoperations progress but the temperature should not'exceed 400 F. Oncethe mold bottomhas attained the desired operating temperature and theproper temperature differential of from 500 to 1200 F. has beenestablished between the upper portion of the mold and the bottom plate,the casting operations can start.

The first step of the casting cycle comprises withdrawing of the airthrough all the ducts either before or just after the upper mold portionhas been seated upon the bottom plate. To form the mold cavity, the topportion of the mold, including the core member, is lowered to establishcontact with the bottom plate and enough pressure exerted on the topportion through the compression springs to prevent any Substantialleakage of air into the mold cavity. The sealing of the mold cavity iseffected by contact of rims 92 or 118 with the bottom plate 44. The airpressure within the mold cavity is reduced from 0.1 to 1.5 p.s.i. belowatmospheric pressure, the particular value chosen in any instance beingdetermined by the height to which the molten metal must be raised.

Upon establishment of the mold cavity and reduction of the air pressuretherein molten metal immediately rises within the cavity under theinfluence of atmospheric pressure until the cavity is filled. Asmentioned hereinabove, the rate of withdrawal of the air may begradually increased to a predetermined maximum value as the filling ofthe mold progresses. Such withdrawal of air and control of the rate ofextraction is effected through suitable valves and pumps not shown.

Upon completion of the filling of the mold cavity, and in some casesbefore all of the metal has frozen therein, a higher vacuum can beestablished at the top of the cavity while retaining substantially thesame degree of evacuation at the bottom of the cavity which was employedduring the filling operation. The higher vacuum should be on the orderof 10 to 14 p.s.i. below atmospheric pressure. The use of a highervacuum at the top of the mold cavity is desirable in the production ofsolid castings since it aids in holding the casting in place in theupper mold portion when it is lifted from the bottom plate and it helpsmaintain a closer contact between the casting and mold top. In makinghollow castings the shrinkage of the solidifying metal around the coreserves to hold the casting securely in the upper mold body and theoverall chill rate is. so high that early application of the high vacuumis not required to shorten the casting cycle. Hence, in making coredcastings, there is generally no need for employing a higher vacuum.Where a higher vacuum is employed, it represents a second step in thecasting cycle.

The next step consists in separating the top portion of the mold fromthe bottom plate. This may be accomplished while a high vacuum is stillmaintained at the top of the mold cavity and while air is beingwithdrawn from the bottom of the mold cavity. If desired, withdrawal ofair from the bottom of the mold cavity may be terminated but this is notnecessary as the reduced air pressure is too small to interfere withmechanical separation of the upper and lower portions of the mold. Theupper portion of the mold with casting therein is elevated to asufficient height by operation of power cylinder 18 to permitadvancement of the sliding frame and tray to a recelvmg position.

In the last step of the cycle after the tray 26 has been moved intoreceiving position, the withdrawal of air is terminated at the top ofthe mold cavity and a positive air pressure is substituted which servesto eject the cast- '11 ing from the mold. It is to be understood thatother means of ejecting the casting may be employed such as mechanicalejector pins.

Upon retraction of the tray 26 with casting 28 or 160 thereon the upperportion of the mold is ready for reseating on the bottom plate and forrepetition of the cycle. a

In the production of hollowcastings the last step must be modified toinclude movement of the core member 100 before ejection occurs. Asmentioned above it is only necessary to raise this member a shortdistance, less than the total height of the mold cavity, in order torelease it from the casting. The core may be lifted before the uppermold assembly is raised or after such movement has begun. However, it isusually desirable to wait until the mold has been elevated beforereleasing the core and thus take advantage of any adherence of thecasting to the core. Ejection can be effected by compressed air asdescribed above or mechanical means may be used.

The cast bodies produced by our process and in our machine possess avery smooth surface free from shrinks and voids. The freezing occurs ata sufficiently rapid rate to produce a fine metallurgical structure. Thefillets formed at the corners eliminate any sharp edges. small stems orprotuberances remain where the casting was gated and these can be easilyremoved or even disregarded in some cases.

It will be appreciated that although the production of circular castingshas been described, other shapes can be made such as oval, polygonal orrectangular. It is also possible to make hollow castings havingdifferent interior and exterior contours. In any case to secure highproduction rates it is desirable to make simple shapes with straight ortapering side walls that facilitate ejection of the casting from themold. In making castings of non-circular shape it may be necessary torearrange the cooling means and change the location of the gates in thebottom plate but such alterations are within the skill of those familiarwith the production of chill castings.

The rate of producing castings can be considerably increased if acasting machine is enlarged to permit the simultaneous casting of anumber of slugs. An upper mold element can be made which includes aplurality of mold cavities and the bottom plate can be made with anynumber of gate openings to register with the mold cavities.

Having thus described our invention and certain embodiments thereof, weclaim:

1. The method of making a light metal chill casting comprising providinga chill mold having at least one gate opening in the bottom thereof,establishing and continuously maintaining the mold bottom at arelatively high temperature and partially immersed in a body of moltenlight metal, the mold bottom being so positioned with reference to thebody of molten metal that the underside of the mold bottom is submergedbut the mold cavity is at all times above the top surface of the moltenmetal and no metal flows into the mold under hydrostatic pressure,artificially cooling the upper portion of the mold whereby a temperaturedifferential is maintained between said upper portion and the bottom,partially evacuating the mold cavity while maintaining the externalwalls of the upper portion of said mold under atmospheric pressure andfilling said mold cavity from the bottom with molten metal drawn fromsaid body of molten metal under the influence of the externalatmospheric pressure, progressively chilling and solidifying the metalfrom the top and sides of the mold cavity toward the gate openings andfinally removing the casting from the mold.

2. The method of makinga light metal c'hill casting comprising providinga chill mold having at least one Only 12 gate opening in the bottomthereof, establishing and continuously maintaining the mold bottom at atemperature between 900 and 1300 F. and partially immersed in a bodyof'molten light metal, the mold bottom being so positioned withreference to the body of molten metal that the mold cavity is at alltimes above the top surface of the molten metal and no metal flows intothe cavity under hydrostatic pressure, artificially cooling the upperportion of the mold whereby a temperature differential of 500 to 1200 F.is maintained between the said upper mold portion and the mold bottom,partially evacuating the mold cavity and filling it from the bottom withmolten metal drawn from said body of molten metal under the influence ofthe, external atmospheric pressure, progressively chilling andsolidifying the metal from the top and sides of the mold cavity towardthe gate openings and finally removing the casting from the mold.

3. The method of making a light metal chill casting comprising providinga chill mold having at least one gate opening in the bottom thereof,establishing and continuously maintaining the mold bottom at atemperature between 900 and 1300 F. and partially immersed in a body ofmolten light metal, the mold bottom being so positioned with referenceto the body of molten metal that the mold cavity is at all times abovethe top surface of the molten metal and no metal flows into the cavityunder hydrostatic pressure,artificially cooling the upper portion of themold whereby the temperature is maintained between and 400 F., reducingthe air pressure within the mold cavity to between 0.1 and 1.5 p.s.i.below atmospheric pressure, filling the mold cavity from the bottom withmolten metal drawn from said body of molten metal under the influence ofthe external atmospheric pressure, progressively chilling andsolidifying the metal from the top and sides of the mold cavity towardthe gate openings and finally removing the casting from the mold.

4. The method according to claim 3 wherein the air pressure. within themold cavity is gradually reduced to a predetermined minimum between 0.1and 1.5 p.s.i. below atmospheric pressure as the mold is being filled.

5. The method of making a light metal chill casting comprising providinga horizontally parted chill mold having at least one gate opening in thebottom of the lower portion, establishing and continuously maintainingthe mold bottom at a temperature between 900 and 1300 F. and partiallyimmersed in a body of molten light metal, the mold bottom being sopositioned with reference to the body of molten metal that the moldcavity is at all times above the top surface of the molten metal and nometal flows into the cavity under hydrostatlc pressure, artificiallycooling the upper portion of the mold whereby the temperature ismaintained between 80 and 400 F., reducing the air pressure within themold cavity to between 0.1 and 1.5 p.s.i. below atmospheric pressure,filling the mold cavity from the bottom with molten'metal drawn fromsaid body of molten metal under the influence of the externalatmospheric pressure, progressively chilling and solidifying the metalfrom the top and sides of the mold cavity toward the gate openings whilesimultaneously further reducing the air pressure in the upper portion ofthe mold cavity, raising the upper portion of the mold with the castingtherein above the lower portion and ejecting the casting from said upperportion.

6. The method of making a light metal chill casting comprising providinga horizontally parted chill mold having at least one gate opening in thebottom of the lower portion, establishing and continuously maintainingthe mold bottom at a temperature between 900 and 1300 F. and partiallyimmersed in a body of molten light metal, the mold bottom being 50positioned with reference to the body of molten metal that the moldcavity is at all times above the top surface of the molten metal and no1 i i I metal ,tipws into the cavity under hydrostatic pressure,artificiallycooling the upper portion of the mold whereby thetemperature'is maintained between 80 and 400 F., partially evacuatingthe mold cavity and filling it from the bottom with molten metal drawnfrom said body of molten metal under theinfluence of the external atmospheric, pressure, progressively chilling andsolidifying the metalfromthe top and sides of the moldcavity toward the gateopenings, raising theupper portion of the mold with the casting therein, terminating theevacuation at the top,of the mold cavity andsubstituting a positive airpressurewhereby the casting is ejected from'the mold.

,7. A machinefor making chill castings wherein the lowerportion of themold is maintained in continuous contact with a body of molten metal andthe mold is filled from the bottom, said machine comprising a mainframe, a mold unit supported from said frame, said mold unit including ahorizontally divided mold the upper portion of which; is movable andcomposed of top and side wall members that "form, respectively, the topand side walls of the mold cavity,-and the lower portion which isstationaryand composed of-aplate member rigidly attached to the mainframe that forms the bottom of the v a 14 a l associated with saidcoreto raise and lower it, said means for raising and lowering the uppermold portion also being capable of establishing sealing contact betweensaid upper portion and the bottom plate member whereby leakage of airfrom the external atmosphere into the mold cavity is prevented, and acontainer below said mold adapted to hold the molten metal supplied tothe mold.

9. A machine for making solid cylindrically shaped castings of lightmetal wherein the lower portion of the mold is maintained in continuouscontact with a body of molten metal and the mold is filled from thebottom, said machine comprising a main frame, a mold unit supported fromsaid frame, said mold unit including a horizontally divided mold theupper portion of which is movable and consists of cylindrical side wallsand a fiat top joined thereto which form the side walls and top of themold cavity, the lower portion of the mold consisting of a fiat platemember rigidly attached to the main frame mold cavity, saidbottom platemember having at least one relatively small gate opening therein forpassage-of molten metal into said mold cavity, the length ofisaid gatebeing-defined by said bottom plate member, cooling means associated withsaid upper portion to maintain it at a lower temperature than the bottomplate member, said upper portion also being provided with separate upperand lower duct and vent systems for withdrawal and admission of air tothe mold cavity, said upper system consisting of a duct terminating inatleast one vent at thetop of the mold cavity and said lower systemconsi'sting of a duct terminating in a vent established by seating oftheupper mold portion on the bottom plate, each duct and vent system beingconnected to means for withdrawing or introducing airto the mold cavity,means connected to said upper mold portion for raising and loweringthe'same and establishing a sealing contact between said upper mold portionand the bottom plate member whereby leakage of air from the externalatmosphere into the mold cavity is substantially preventediand acontainer below said mold adapted to hold the molten metal supplied tothe mold.

8. A machine for making chill castings wherein the lower portion of themold is maintained in continuous contact with a body of molten metal andthe mold is filled from the bottom, said machine comprising a mainframe, a mold unit supported from said frame, said mold unit including ahorizontally divided mold the upper portion of which is movable andcomposed of top and side wall members that form, respectively, the topand side walls of the mold cavity, the side wall members consisting of afixed outer member and the inner wall consisting of a movable coremember, the lower portion of said mold being stationary and composed ofa plate member rigidly attached to the main frame that forms the bottomof the mold cavity, said bottom plate member having at least onerelatively small gate opening therein for passage of molten metal intothe mold cavity, the length of sa d gate being defined by said bottomplate member, cooling means associated with said upper mold portion,including the core, to maintain it at a lower temperature than thebottom plate member, said upper portion also being provided withseparate upper and lower duct and vent systems for the withdrawal andadmission of air to the mold cavity, said upper system consisting of aduct terminating in vents at the top of the mold cavity and said lowersystem consisting of a duct terminating in a vent established by seatingthe outer fixed side wall mold member on the bottom plate member, eachduct and vent system being connected to means for withdrawing andintroducing air to the mold cavity, means connected to said upper moldportion for raising and lowering the same and means the bottom of themold cavity, said bottom plate member having at leastone relativelysmall gate opening therein for passage of molten metal into the moldcavity, the length of said gate being defined by saidbottom platemember, a circumferential rim at the base of the circular side wallmember which establishes sealing engagement with the bottom plate memberunder pressure applied to the upper mold portion, liquid coolantpassageways associated with said side and top members of the upper molda portion whereby the temperature of said upper portion tem. consistingof a duct communicating with a circumferential vent at the junction ofthe top and side wall members of the upper mold portion, and the lowersystem consisting of a duct. communicating with an annular groove-in thebase of the mold side wall member and said groove further communicatingwith the mold cavity through a circumferential vent at the junction ofthe side wall member and the bottom plate member when the upper moldportion isseated on the bottom plate, each duct and vent system beingconnected to means for withdrawing and introducing air to the moldcavity, fluid power means connected to said upper mold portion forraising and lowering the same and establishing a sealing contact betweenthe circumferential rim at the base of the side wall member and thebottom plate member whereby leakage of air from the external atmosphereinto the mold cavity is substantially prevented, and a container belowsaid mold adapted to hold the molten metal supplied to the mold.

10. A machine for making hollow cylindrically shaped mold is maintainedin continuous contact with a body of molten metal and the mold is filledfrom the bottom, said machine comprising a main frame, a mold unitsupported from said frame, said moldunit including a horizontallydivided mold the upper portion of which is movable and composed of anouter cylindrical side wall member, flat top member joined to said sidewall and a cylindrically shaped movable central core member, and thelower portion of said mold consisting of a stationary flat plate memberrigidly attached to the main frame having a plurality of relativelysmall gate openings therein for passage of molten metal into the moldcavity, the length of said gates being defined by the thickness of saidstationary flat plate member, liquid coolant passageways associated withsaid outer cylindrical side wall member and said core member wherebythey are maintained at a temperature below that of the bottom platemember, said upper por tion of the mold also being provided withseparate upper and lower duct and vent systems for the withdrawal andadmission of air to the mold cavity, said upper system consisting of aduct terminating in a. circumferential vent at the junction of the sidewall with the mold top member and in a second vent at the junction ofthe top mem% ber with the central core member, the lower duct and ventsystem consisting of a duct terminating in an annular groove in the baseof the side wall and said groove communicating with the mold cavitythrough a circumferential vent at the junction of the side wall memberwith the bottom plate when the upper mold portion is seated on thebottom plate member, each duct and vent system being connected to meansfor withdrawing and introduc ing air to the mold cavity, fiuid powermeans connected to said upper mold portion for raising and lowering itand establishing a sealing contact between said side wall and bottomplate member whereby leakage of air from the external atmosphere intothe mold cavity is substantially prevented, a second fluid power meansconnected to said central core member for raising and lowering it, and acontainer below said mold adapted to hold molten metal supplied to themold.

11. A machine for making chill castings in combination with a castingtransfer device wherein the lower portion of the mold in the castingmachine is maintained in continuous contact with a body of molten metaland the mold is filled from the bottom, said machine comprising a mainframe, a mold unit supported from'sai'd frame, said mold unit includinga horizontally divided mold the upper portion of which is movable andcomposed of top and side wall members that form, respectively, the topand side walls of the mold cavity, and the lower portion which isstationary and composed of a plate member rigidly attached to the mainframe that forms the bottom of the mold cavity, said bottom plate memberhaving at least one relatively small gate opening therein for passage ofmolten metal into said mold cavity, the length of said gate beingdefined by said bottom plate member, cooling means associated with theupper mold portion to maintain it at a lower temperature than the bottomplate member, said upper portion also being pro vided with separateupper and lower duct and vent systems for withdrawal and admission ofair to the mold cavity, said upper system consisting of a ductterminating in at least one vent at the top of the mold cavity and saidlower system consisting of a duct terminating in a vent established byseating of the upper mold portion on the bottom plate member, each "ductandvent system being connected to means for withdrawing or-introducingair to the mold cavity, means connected with said upper mold portion forraising and lowering the same and establishing a sealing contact betweensaid upper portion and the bottom plate member whereby leakage of airfrom the external atmosphere into the mold cavity is substantiallyprevented, and a casting transfer device positioned at one side of thecasting machine and operatively associated therewith, said transferdevice comprising a frame and a reciprocable tray mounted-thereon andmeans for advancing and retracting said tray, said tray being located atan elevation with respect to the mold unit such that in advancedposition it comes between the upper and lower mold portions when theupper portion is in raised position to receive the casting ejected fromthe raised upper mold portion. 7

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